1. Field of the Invention
The invention is in the field of manufacturing processes related to material removal. It particularly relates to optical control methods and apparatus concerned with such manufacturing processes in solid state device fabrication.
2. Brief Description of the Prior Art
There are, in commercial use, a number of etching, stripping, or other material removal operations which employ plasma discharges and charged particles produced by such discharges. Such processes are becoming more and more widely used in the fabrication of solid state devices, to displace wet chemical processing. In these processes the surface to be treated is exposed to a plasma discharge or to a beam of accelerated particles from the plasma. Most of these processes fall into two main groups. In the first of these groups the removal of material from the body being treated is produced by a chemical reaction between active species in the plasma and the material of the body, with the formation of volatile reaction products. The volatile products are then pumped away. The other principal group involves the removal of material from the body being treated, by momentum transfer from accelerated particles in the plasma. In either case it is commercially observed that light in the infrared, visible and ultraviolet regions of the spectrum is produced in the space surrounding the body. It has been noted in the past that both the intensity and color of the emitted light, in many of these processes, changes during the processing operation. However, several different chemical and physical phenomena are occurring simultaneously in the discharge region, so that it may be difficult to draw exact conclusions from the observation of the emitted light.